1. Field of the Invention
The present invention relates to a wire bonding machine for bonding opposite ends of wires to a semiconductor chip and a lead frame, respectively, and more particularly to a heat block of such a wire bonding machine in which an inner lead heating part thereof is heated at a relatively higher heating temperature than that of a chip heating part thereof so that the bonding effect is improved at the bonding portions between the wires and inner leads of the lead frame without occurrence of damage of the semiconductor chip due to the heating temperature.
2. Description of The Prior Art
Conventionally, wire bonding machines are widely used for connecting a semiconductor chip to a lead frame by bonding opposite ends of a plurality of wires, such as gold wires, to a semiconductor chip and inner leads of the lead frame, respectively, for manufacturing a semiconductor package. The wire bonding machine is generally provided with a heat block for providing a bonding heat for the bonding portions between the opposite ends of the wires and the semiconductor chip and the inner leads of the lead frame.
With reference to FIG. 1 which shows a known heat block of a wire bonding machine according to the prior art, the heat block includes upper and lower heating blocks 10 and 20 of which the upper heating block 10 is provided thereon with a chip heating part 11 for allowing a semiconductor chip (not shown) and one end of each wire to be laid thereon so as to be heated and bonded and an inner lead heating part for allowing the other end of the wire and the inner leads of the lead frame (not shown) to be laid thereon so as to be heated and bonded.
In addition, the lower heating block 20 is provided with a pair of receiving holes 20a and 20b formed as longitudinally machined and spaced apart from each other in parallelism and adapted for receiving a heater 31 and thermocouple 33, respectively.
In bonding operation, the heat block is heated by the heater 31 at a predetermined temperature, then receives thereon the lead frame which has been provided with a semiconductor chip on the heating parts 11 and 12 of the upper heating block 10, thereafter, the lead frame on the heating parts 11 and 12 is clamped by a clamp 43. In result, the capillary chip is connected to the inner leads of the lead frame by bonding both ends of the wires to the chip and the inner leads.
However, the known heat block has disadvantage in that the heating temperatures of respective heating parts are controlled at the same time by means of the single thermocouple 33 under the condition of being controlled by a temperature control device so that it is impossible to control a first heating temperature for bonding one end of each wire to the chip differently from a second heating temperature for bonding the other end of the wire to each inner lead of the lead frame. In other words, the first heating temperature in bonding operation is generally desired to be controlled at about 200.degree..+-.10.degree. C.
Here, it is well known that the higher heating temperature is maintained, the high bonding effect is accomplished, thus it is desired to control the heating temperature for bonding the wire to the chip and the inner lead to be higher than the above temperature of 200.degree..+-.10.degree. C. However, the heating temperature above 200.degree..+-.10.degree. C. will damage the semiconductor chip due to a relatively lower heat resistance of the semiconductor chip so that the heat block can not be heated to a temperature above 200.degree..+-.10.degree. C. In result, the known heat block has disadvantage in that it can not provide a good bonding effect in the bonding portion between the wires and the inner leads of the lead frame due to the relatively lower heating temperature of about 200.degree..+-.10.degree. C.